Fig. 2. (a) Fluorescence emission of CHS2 under 808 nm excitation; (b) photostability of CHS2 in water, PBS and serum under 808 nm laser illumination (105 mW cm^–2) for 1 h; (c) photostability of ICG vs.CHS2 under 808 nm laser illumination (82 mW cm^–2) for 1 h; (d) cellular toxicity of different concentrations of CHS2 in U87MG cell lines.